This invention relates to a power management system. More specifically, this invention relates to a circuit and an associated power management technique to detect and respond to changes in the power supplied to a system of one or more integrated circuit devices.
Microprocessor and microcontroller based systems are obviously dependent upon a continuous supply of electrical power for their operation, which may be from a line source, a battery, a local generator, or the like. A primary effect of an insufficient voltage level being supplied to integrated circuits of such a system is the loss of data in volatile memory. Inevitable occasional disruptions in the power supply are desirably handled in a manner that minimizes such effects. Such power disruptions include short power glitches, a total removal of power, such as occurs during power outages when a line source is used or when a battery is removed from a battery supplied system, and, in the case of a battery supply, when the voltage of the battery declines over time below a level sufficient to operate the circuits. Further, a rapid change in voltage supply level may also damage integrated circuits if not handled properly.
There are many standard approaches for eliminating or reducing such undesirable effects of a power supply interruption. For example, when a digital clock is unplugged, oftentimes the clock is equipped with a backup battery to permit the clock to continue operating. The clock might continue to work for about thirty minutes, obviating the need for reprogramming once it is plugged in again. Likewise, some television sets are equipped with a battery to permit storage of the contents of programmed channels or other user defined values. Thus, the television does not have to be reprogrammed once the power is resupplied. While the use of a battery as a backup power source is advantageous, it is inefficient. The battery must be periodically replaced, which is potentially expensive, and the back-up battery may not always be charged enough to properly compensate for a loss of power. A back-up battery is therefore unreliable and not cost effective for use in power management.
Another situation that is encountered is a complete loss of power where a battery backup cannot be used or is not practical. And in battery supplied systems, such as with a hand held television remote control device, the effects of a low battery voltage or the removal of the batteries altogether provides a disruption which must somehow be handled.
Therefore, it is a general object of the invention to provide a novel power management system which will obviate or minimize difficulties of the type previously described.
It is a specific object of the invention to provide a power management system which detects changes in power supply voltage.
It is yet another object of the invention to provide a circuit for use in a power management system which does not require a power source other than the main power input.